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How can i create a dynamic string format in C#

I have as input the string format CST-000000 and an integer with value 1
Upon using
string result = string.Format("CST-000000", 1);
the expected result should be CST-000001 instead of CST-000000
How could i create this string format dynamically?
For example
- CST-000 should produce CST-001
- HELLO000 should produce HELLO001
- CUSTOMER0000 should produce CUSTOMER0001

Assuming that:
You receive your format string from somewhere and you can't control what it looks like
Your format string ends with 1 or more zeros
If the format string is e.g. CST-00000 and your value is 123, you want the result to be CST-00123
You can do something like this:
Inspect your format string, and separate out the stuff at the beginning from the zeros at the end. It's easy to do this with Regex, e.g.:
string format = "CST-000000";
// "Zero or more of anything, followed by one or more zeros at the end of the string"
var match = Regex.Match(format, "(.*?)(0+)$");
if (!match.Success)
{
throw new ArgumentException("Format must end with one or more zeros");
}
string prefix = match.Groups[1].Value; // E.g. CST-
string zeros = match.Groups[2].Value; // E.g. 000000
Once you have these, note the "Zero placeholder" in this list of custom numeric format strings -- you can write e.g. 123.ToString("0000") and the output will be 0123. This lets you finish off with:
int value = 123;
string result = prefix + value.ToString(zeros);
See it on dotnetfiddle

String.Format requires a placeholder {n} with a zero-based argument number. You can also add it a format {n:format}.
string result = String.Format("CST-{0:000000}", 1);
You can also use String interpolation
string result = $"CST-{1:000000}"
The difference is that instead of a placeholder you specify the value directly (or as an expression). Instead of the Custom numeric format string, you can also use the Standard numeric format string d6: $"CST-{1:d6}"
If you want to change the format template dynamically, String.Format will work better, as you can specify the format and the value as separate arguments.
(Example assumes an enum FormatKind and C# >= 8.0)
int value = 1;
string format = formatKind switch {
FormatKind.CstSmall => "CST-{0:d3}",
FormatKind.CstLarge => "CST-{0:d6}",
FormatKind.Hello => "HELLO{0:d3}",
FormatEnum.Customer => "CUSTOMER{0:d4}"
};
string result = String.Format(format, value);
Also note that the value to be formatted must be of a numeric type. Strings cannot be formatted.
See also: Composite formatting

It seems .toString("CST-000"), .toString("HELLO000") and so on, does the trick.

ToString and String.Format can do much more than use predefined formats.
For example :
string result = string.Format("CST-{0:000000}", 1);
string result = 1.ToString("CST-000000");
Should both do what you want.
(Of course you could replace "1" by any variable, even a decimal one).

Get DateTime from FileName

I have a file named test-2000_01_02-10_12_14.xml.
How do I only get the date from the file?
I was able to get the date if the file has this name: 2000_01_02-10_12_14
with this (b is a StorageFile):
DateTime dateVal;
bool parsed = DateTime.TryParseExact(b.DisplayName,
"yyyy_MM_dd-H_mm_ss",
System.Globalization.CultureInfo.InvariantCulture,
System.Globalization.DateTimeStyles.None,
out dateVal);
I then tried to change yyyy_MM_dd-H_mm_ss to something like this *-yyyy_MM-dd-H-mm_ss but it does not seem to be the solution

There are a boatload of ways to do this, it really rather depends on how regular the naming of your files is - is there always some junk text followed by a hyped, then the year?
Post up another 10 different examples if you want more tailored advice. Here's a way for the one you've posted:
DateTime.TryParseExact(
Path.GetFileNameWithoutExtension(b.DisplayName.Substring(b.DisplayName.IndexOf('-')+1)),
"yyyy_MM_dd-H_mm_ss",
System.Globalization.CultureInfo.InvariantCulture,
System.Globalization.DateTimeStyles.None,
out dateVal
);
This uses Substring with only one argument (no length) to remove everything after the first hyphen up to the end of the string, and GetFileNameWithoutExtension to remove the .xml - this effectively turns anythinghere-2000_01_01-00_00_00.xml into 2000_01_01-00_00_00 ready for parsing
I could also have gone for a .Remove("last index of period") type thing but it does get a bit messy because you have to subtract the start Index of the hyphen etc
MJWill's comment about splitting on hyphen is also a good one - you could split then take the [1] and [2] indexes and join then back together for parsing..
Lastly don't forget that the file itself might have a created date that is already a good candidate for the date of creation rather than the filename (which might be mangled by humans) so long as it hasn't been transmitted somewhere and re-saved. Take a look at the FileInfo.CreationTime property for that - https://learn.microsoft.com/en-us/dotnet/api/system.io.fileinfo?view=netframework-4.8

First, we have to extract (match) the datetime part from a file name:
using System.Text.RegularExpressions;
...
// Aggravated task: dots and minuses within file's name
string source = #"bla-bla-bla-test.me-2000_01_02-10_12_14.xml";
string datetime = Regex.Match(
Path.GetFileNameWithoutExtension(source),
"[0-9]{4}_[0-9]{2}_[0-9]{2}-[0-9]{2}_[0-9]{2}_[0-9]{2}$").Value;
Then we can parse it
if (DateTime.TryParseExact(
datetime,
"yyyy_MM_dd-H_m_s",
CultureInfo.InvariantCulture,
DateTimeStyles.AssumeLocal,
out DateTime result) {
// result is the parsed date
}
else {
// File doesn't contain valid date and time
}

I would suggest you to use regular expression assuming that your file name will be always following the same format you can do something like this:
var pattern = #"\d{4}_\d{2}_\d{2}-\d{2}_\d{2}_\d{2}";
var fileName = "test-2000_01_02-10_12_14.xml";
var match = new Regex(pattern);
var result = match.Match(fileName);
if (result.Success)
{
DateTime.TryParseExact(result.Value,
"yyyy_MM_dd-HH_mm_ss",
System.Globalization.CultureInfo.InvariantCulture,
System.Globalization.DateTimeStyles.None,
out DateTime dateVal);
}

How to remove DateTime substring from string

I have a bunch of strings, some of which have one of the following formats:
"TestA (3/12/10)"
"TestB (10/12/10)"
The DateTime portion of the strings will always be in mm/dd/yy format.
What I want to do is remove the whole DateTime part including the parenthesis. If it was always the same length I would just get the index of / and subtract that by the number of characters up to and including the (. But since the mm portion of the string could be one or two characters, I can't do that.
So is there a way to do a .Contains or something to see if the string contains the specified DateTime format?

You could use a Regular Expression to strip out the possible date portions if you can be sure they would consistently be in a certain format using the Regex.Replace() method :
var updatedDate = Regex.Replace(yourDate,#"\(\d{1,2}\/\d{1,2}\/\d{1,2}\)","");
You can see a working example of it here, which yields the following output :
TestA (3/12/10) > TestA
TestB (10/12/10) > TestB
TestD (4/5/15) > TestC
TestD (4/6/15) > TestD

You could always use a regular expression to replace the strings
Here is an example
var regEx = new Regex(#"\(\d{1,2}\/\d{1,2}\/\d{1,2}\)");
var text = regEx.Replace("TestA (3/12/10)", "");

Use a RegEx for this. I recommend:
\(\d{1,2}\/\d{1,2}\/\d{1,2}\)
See RegExr for it working.

Regex could be used for this, something such as:
string replace = "TestA (3/12/10) as well as TestB (10/12/10)";
string replaced = Regex.Replace(replace, "\\(\\d+/\\d+/\\d+\\)", "");

If I'm understanding this correctly you want to just acquire the test name of each string. Copy this code to a button click event.
string Old_Date = "Test SomeName(3/12/10)";
string No_Date = "";
int Date_Pos = 0;
Date_Pos = Old_Date.IndexOf("(");
No_Date = Old_Date.Remove(Date_Pos).Trim();
MessageBox.Show(No_Date, "Your Updated String", MessageBoxButton.OK);
To sum it up in one line of code
No_Date = Old_Date.Remove(Old_Date.IndexOf("(")).Trim();

How to replace a string with another

I'd like to make a program that isn't sensitive to the character , or . as input, in order to make some calculations without thinking about which symbol I should use to separate integer part from fractional part.
The only way i can imagine is to recognize the input string, check if there's a . and replace it with a , as my cultureType only accepts ,.
The problem is that I don't have any idea to make it, can someone help me?

if(inputString.Any(x => x == '.'))
{
inputString = inputString.Replace('.', ',');
}

I'm guessing (it's not in your question) that you're trying to parse a decimal, and the number may have a decimal separator and no thousand separator, and it might be a , and it might be a . A possible heuristic to guess which one it is, is to check the last occurrence of either.
That could be done by
string input = "123.456.496,58"; //or 123,456,789.58
int lastComma = input.LastIndexOf(",");
int lastPeriod = input.LastIndexOf('.');
NumberFormatInfo format = new NumberFormatInfo();
if (lastComma > lastPeriod) {
format.NumberDecimalSeparator = ',';
format.NumberGroupSeparator = '.';
} else {
format.NumberDecimalSeparator = '.';
format.NumberGroupSeparator = ',';
}
double parsed = Double.Parse(intput, format);
this fails when there is a group separator after the decimal separator, and other heurisics could be employed to change it (i.e. if there is only one non-numeric character, that one is the decimal separator. If there are multiple non-numeric special characters, and one of them only occurs once, that is the decimal separator)
In the end parsing a string with an unknown format will require some guesswork.
If you're not trying to parse numbers, but are doing something different entirely, disregard this answer, and pick one of the others.

if (yourString.Contains(".")) { youString = yourString.Replace(".", ","); }

parsing a string into int/long using custom format strings

In C#.Net, here's a simple example of how to format numbers into strings using custom format strings:
(example taken from: http://www.csharp-examples.net/string-format-int/)
String.Format("{0:+### ### ### ###}", 447900123456); // "+447 900 123 456"
String.Format("{0:##-####-####}", 8958712551); // "89-5871-2551"
Is there a way to convert this formatted string back into a long/integer ? Is there someway to do this :
long PhoneNumber = Int32.Parse("89-5871-2551", "{0:##-####-####}");
I saw that DateTime has a method ParseExact which can do this work well. But I did not see any such thing for int/long/decimal/double.

You can regex out all of the non numeric numbers, and what you're left with is a string of numbers that you can parse.
var myPhoneNumber = "89-5871-2551";
var strippedPhoneNumber = Regex.Replace(myPhoneNumber, #"[^\d]", "");
int intRepresentation;
if (Int32.TryParse(strippedPhoneNumber, out intRepresentation))
{
// It was assigned, intRepresentation = 8958712551
// now you can use intRepresentation.
} else {
// It was not assigned, intRepresentation is still null.
}

Well, you can always do
long PhoneNumber = Int32.Parse("89-5871-2551".
Replace(new char[]{'-','+',whatever..}).Trim());
By the way, considering that you're parsing a string received from some IO, I would suggest to use more secure (in terms of conversion) Int32.TryParse method.
The way like you described doesn't actually exist.

Just Regex out all of the non-numeric characters, then parse that string.